Comparative Radiation Death Kinetics of Clostridium botulinum Spores at Low-Temperature Gamma Irradiation

Spores of Clostridium botulinum 33A were irradiated with ⁶⁰Co gamma rays in 0.067 M Sorensen phosphate buffer (pH 7.0) at -196, -140, -80, -30, or 5 C and incubated in recovery broth for 30 days at 30 C, thus simulating an inoculated pack and eliciting "partial spoilage" data. Resistance of the spores decreased linearly with increasing temperature. A simple empirical equation was derived to predict D values for any desired temperature. An Arrhenius plot of the D value-radiation temperature profile indicated that the death kinetics is not first order. Comparison of the data in this model system with those previously observed in beef indicates a similar radiation death pattern, except that resistance of the spores was somewhat more (1.6-fold) temperature dependent, although significantly more resistant, in the beef. A comparison of the D value-temperature relationship of Streptoccus faecium a21, obtained earlier, with strain 33A in the same model system indicated that the spores were considerably less resistant below -20 C and much more resistant above this radiation temperature.